Technological development and increased demand for mobile devices have led to rapid increase in the demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries having high energy density and high discharge voltage have been extensively studied and are now commercially available and widely used. Lithium secondary batteries are the most commonly used due to superior electrode life and high rapid-charge/discharge efficiency.
Lithium-containing cobalt oxide (LiCoO2) is typically used as a cathode active material for lithium secondary batteries and use of lithium-containing manganese oxides such as LiMnO2 having a layered crystal structure and LiMn2O4 having a spinel crystal structure and lithium-containing nickel oxides (LiNiO2) is also under consideration.
Among such cathode active materials, LiCoO2 is currently widely used due to superior general properties such as excellent cycle characteristics, but has disadvantages such as low safety and high cost due to limited resource availability of cobalt as a raw material. Lithium nickel-based oxides such as LiNiO2 have problems such as high manufacturing cost, swelling caused by gas generation in batteries, low chemical stability, and high pH although they are cheaper than LiCoO2 and exhibit high discharge capacity when charged to 4.25V.
Lithium manganese oxides such as LiMnO2 and LiMn2O4 have attracted a great deal of attention as cathode active materials capable of replacing LiCoO2 due to advantages such as natural abundance of the raw materials and the use of eco-friendly manganese. Among these lithium manganese oxides, LiMn2O4 has advantages such as relatively low price and high output, but has lower energy density than LiCoO2 and three-component active materials.
When Mn in LiMn2O4 is partially replaced by Ni to overcome such disadvantages, an operating potential of about 4.7 V, higher than the original operating potential of about 4 V, is achieved. A spinel material having a composition of Li1+aNixMn2-xO4-z(0≤a≤0.1, 0.4≤x≤0.5, 0≤z≤0.1) has a high potential and, as such, is ideally suited for use as a cathode active material for middle or large-scale lithium ion batteries such as electric vehicles that require high energy and high output performance.
Lithium transition metal active materials containing two or more types of materials such as Ni and Mn are not easily synthesized by simple solid-state reaction. In a known technique, a transition metal precursor prepared by coprecipitation or the like is used as a precursor to prepare such lithium transition metal active materials.
However, a transition metal precursor for preparing the spinel material is not easily synthesized by coprecipitation since the transition metal precursor has a high content of Mn such that oxidation easily occurs due to oxygen dissolved in an aqueous transition metal solution.
Thus, a lithium composite transition metal oxide having satisfactory performance and a precursor for preparing such a lithium composite transition metal oxide have yet to be developed.